Techniques for establishing subscriber sessions on an access network using DHCP

ABSTRACT

Techniques for supporting subscriber sessions for access to an IP network include receiving from a first node at a different second node, a Dynamic Host Configuration Protocol (DHCP) formatted echo-request message. The echo-request message includes a DHCP option field that holds data that indicates an echo-request type. In response to receiving the echo-request message, the second node sends to the first node a DHCP formatted echo-reply message that corresponds to the echo-request message. The echo-reply message includes a DHCP option field that holds data that indicates an echo-reply type. When received by the first node, the echo-response message causes the first node to determine a connected state with the second node. Point to Point Protocol (PPP) keep-alive messages between a customer premises node and a remote access server gateway to an IP network may be replaced by these DHCP echo-request and echo-reply messages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______(Attorney Docket Np. CIS001-039 (Seq. 13197)), filed MMMM XX, 2006(referenced hereinafter as Townsley) the entire contents of which arehereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to migrating point to point protocol (PPP)functions for customer access of a wide area network to the InternetProtocol (IP).

2. Description of the Related Art

Networks of general purpose computer systems and special devicesconnected by external communication links are well known. The networksoften include one or more network devices that facilitate the passage ofinformation between the computer systems. A network node is a networkdevice or computer system or special device connected by thecommunication links.

Information is exchanged between network nodes according to one or moreof many well known, new or still developing protocols. In this context,a protocol consists of a set of rules defining how the nodes interactwith each other based on information sent over the communication links.The protocols are effective at different layers of operation within eachnode, from generating and receiving physical signals of various types,to selecting a link for transferring those signals, to the format ofinformation indicated by those signals, to identifying which softwareapplication executing on a computer system sends or receives theinformation. The conceptually different layers of protocols forexchanging information over a network are described in the Open SystemsInterconnection (OSI) Reference Model. The OSI Reference Model isgenerally described in more detail in Section 1.1 of the reference bookentitled Interconnections Second Edition, by Radia Perlman, publishedSeptember 1999, which is hereby incorporated by reference as thoughfully set forth herein.

Communications between nodes are typically effected by exchangingdiscrete packets of data. Each packet typically comprises 1] headerinformation associated with a particular protocol, and 2] payloadinformation that follows the header information and contains informationthat may be processed independently of that particular protocol. In someprotocols, the packet includes 3] trailer information following thepayload and indicating the end of the payload information. The headerincludes information such as the source of the packet, its destination,the length of the payload, and other properties used by the protocol.Often, the data in the payload for the particular protocol includes aheader and payload for a different protocol associated with a different,higher layer of the OSI Reference Model. The header for a particularprotocol typically indicates a type for the next protocol contained inits payload. The next protocol is said to be encapsulated in theparticular protocol. The headers included in a packet traversingmultiple heterogeneous networks, such as the Internet, typically includea physical (layer 1) header, a data-link (layer 2) header, aninternetwork (layer 3) header and a transport (layer 4) header, asdefined by the Open Systems Interconnection (OSI) Reference Model.

Some protocols span the layers of the OSI Reference Model. For example,the Ethernet local area network (LAN) protocol includes both layer 1 andlayer 2 information. The International Electrical and ElectronicsEngineers (IEEE) 802.3 protocol, an implementation of the Ethernetprotocol, includes layer 1 information and some layer 2 information.

One such layer 2 protocol is the Point to Point Protocol (PPP) between ahost computer on a local area network and a network node that providesaccess to a wide area network, such as the Internet. Some protocols,including PPP, pass protocol-related information among two or morenetwork nodes in special control packets that are communicatedseparately and which include a payload of information used by theprotocol itself rather than a payload of data to be communicated foranother application. These control packets and the processes at networknodes that utilize the control packets are said to be in anotherdimension, a “control plane,” distinct from the “data plane” dimensionthat includes the data packets with payloads for other applications. Forexample, authentication information used to authenticate users and layer3 address assignment information used by routers to direct data packetsaccording to their layer 3 addresses are passed between nodes in PPPcontrol messages in the PPP control plane.

PPP provides a standard method for transporting any of multiple protocoldata packets (also called frames, datagrams and cells, and usedinterchangeably herein) over point-to-point links. PPP is defined in anInternet Engineering Task Force (IETF) request for comments document(RFC) numbered 1661, dated July 1994, the entire contents of which arehereby incorporated by reference as if fully set forth herein. Copies ofRFC 1661 and other RFCs cited below are available at the World Wide Webdomain ietf.org. PPP has been used extensively to connect users at ahome site to a remote network using modems and telephone copper loopinfrastructure. PPP provides a robust control plane for signaling linecharacteristics, network protocol parameters, and user-levelauthentication. In large service provider networks, the userauthentication models are generally well entrenched, including, but notlimited to, custom-built applications for communicating policy tonetwork equipment and to track billing information.

For applications in which multiple hosts on a shared Ethernet establishPPP sessions to multiple destinations via one or more bridging modems, aPPP over Ethernet (PPPOE) specification has been developed. PPPoE isintended to be used with broadband remote access technologies thatprovide a bridged Ethernet topology, when access providers wish todistinguish different users connected via the same modem to the remotenetwork. PPP provides this distinction by opening different sessionswith different users. PPPoE is described in IETF RFC 2516, the entirecontents of which are hereby incorporated by reference as if fully setforth herein. After establishing a PPP session, IP data packets are sentencapsulated in PPPoE.

There is a trend among network service providers to move to Ethernet andIP as the only layer two and layer three protocols between end nodes ata user site and end nodes on the remote network to which access issought. One reason given for this trend is a desire to make use ofIP-based quality of service (QoS) capabilities available in accessnetwork equipment. Another reason given is to reduce complexity becausedata packets can be transmitted from one portion of the networkinfrastructure to another without translating between layer 2 protocols.Another reason given is that using IP over Ethernet will improve thebandwidth utilization per transmitted frame due to a lower protocoloverhead.

One approach is to eliminate PPP and PPPoE; and provide the PPPfunctions using IP-based functions. For example, it has been proposed touse International Electrical and Electronics Engineers standard 802.1xor web portal methods for authentication, and to use the Dynamic HostConfiguration Protocol (DHCP) for assigning IP addresses. Ajustification offered for this approach is that, when all encapsulateddata packets are IP, the multi-protocol encapsulation capability of PPPis not valuable.

There are some disadvantages to eliminating PPP. For example, web portalbased authentication has drawbacks in that it requires a specificapplication (web browser) to be activated before anything can happen.The existing IP-based functions do not perform all the functionsperformed by PPP. Some of these protocols would have to be extended toperform the missing functions. For example, DHCP would have to beextended to perform user authentication and integration with anauthorization server, and include a connection “keep-alive” mechanism,among other tasks, in order to encompass all of the functionality thatPPP offers today.

In one approach, described in RFC 3118 on DHCP authentication, amechanism is presented that is directed to authenticating the DHCPmessages themselves to ensure that they did not get altered in transmit,rather than authenticating the user.

PPP provides a “keep-alive” mechanism for detecting when a session isactive and available so that reallocation of an IP address or billingcan take place on session termination. DHCP does not have any mechanismtoday apart from a lease timeout. In one approach, DHCP is used withvery short lease times, e.g., as short as 5 seconds. A problem with thisapproach is that devices for users who engage in sessions that lastlonger than the lease time have to negotiate new leases with the DHCPserver, increasing the consumption of network resources both in terms oftraffic volume and computational time at a node that hosts a DHCPserver.

An Address Resolution Protocol (ARP) has been developed and deployed todetermine what nodes have what IP addresses. An ARP request is broadcaston a link, and every node on the link responds with its IP address. Inone approach ARP is used to determine whether an IP address known to beon a given link is still active. A problem with this approach is thatany recipient of the broadcast may respond. A mls-configured or roguerecipient may respond with the IP address of a disconnected node andthereby mask the actual loss of connection state.

Also, as pointed out above, especially in large service providernetworks, PPP-based functions are generally well entrenched withprovider-specific extensions. For example, some provider-specificextensions provide authorization to determine whether an authentic useris in good standing for receiving one or more services, e.g., forpaid-up basic services, for voice services, or for a particular qualityof service, or some combination. Many of these extensions involve aBroadband Remote Access Server (BRAS) hooking into an Authentication,Authorization, Accounting (AAA) server like the Remote AuthenticationDial-In-ervice (RADIUS) server. Neither RFC 3118 nor DHCP are directedto determining whether an authentic user is actually authorized toaccess any particular services on the network, nor involve hooking intoan AAA server. A wholesale replacement of general PPP functions with IPwill not address any provider-specific extensions. Some transitionperiod is needed to give the provider time to adapt theprovider-specific extensions to the IP mechanisms.

Based on the foregoing, there is a clear need for techniques thatmigrate one or more PPP functions to IP over Ethernet infrastructure butthat do not suffer all the disadvantages of the prior art approaches. Inparticular there is a need to provide session keep-alive and sessiontermination detection functions in DHCP to replace these functions inPPP.

The approaches described in this section could be pursued, but are notnecessarily approaches that have been previously conceived or pursued.Therefore, unless otherwise indicated herein, the approaches describedin this section are not to be considered prior art to the claims in thisapplication merely due to the presence of these approaches in thisbackground section.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram that illustrates a remote access network,according to an embodiment;

FIG. 2 is a block diagram that illustrates a packet of data communicatedover a network;

FIG. 3 is a block diagram that illustrates a DHCP packet of datacommunicated over a network;

FIG. 4 is a block diagram that illustrates an end user host according anembodiment;

FIG. 5 is a block diagram that illustrates a BRAS host, according anembodiment;

FIG. 6 is a flow diagram that illustrates a method at a DHCP sessionprocess, according to an embodiment; and

FIG. 7 is a block diagram that illustrates a computer system configuredas an intermediate network node upon which an embodiment of theinvention may be implemented.

DETAILED DESCRIPTION

A method and apparatus and system are described for migrating at leastone of PPP session keep-alive functionality and PPP session terminationfunctionality to DHCP. In the following description, for the purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order to avoidunnecessarily obscuring the present invention.

In various embodiments described herein, techniques are provided thatperform at least some PPP control plane functionality while utilizingDHCP, itself a purely control plane protocol. In the followingdescription, embodiments are described primarily in the context ofmigrating the PPP session functionality to DHCP between a customerpremises end node and a Broadband Remote Access Server (BRAS) across anaccess network. However, the invention is not limited to theseembodiments. In other embodiments, the functionality is provided by DHCPformatted messages sent between any node and any other node across an IPnetwork. In some embodiments, DHCP messages are used in NetworkAdmission Control (NAC) for sessions with any host connected to anenterprise network.

DHCP is based on a client-server model of network communications, wellknown and widely used in the art. According to the client-server model,a client process sends a message including a request to a serverprocess, and the server process responds by providing a service. Theserver process may also return a message with a response to the clientprocess. Often the client process and server process execute ondifferent computer devices, called hosts, and communicate via a networkusing one or more protocols for network communications. The term“server” is conventionally used to refer to the process that providesthe service, or the host computer on which the process operates.Similarly, the term “client” is conventionally used to refer to theprocess that makes the request, or the host computer on which theprocess operates. As used herein, the terms “client” and “server” referto the processes, rather than the host computers, unless otherwise clearfrom the context. In addition, the process performed by a server can bebroken up to run as multiple servers on multiple hosts (sometimes calledtiers) for reasons that include reliability, scalability, redundancy, orother advantages, or some combination.

According to the DHCP client server model, a DHCP client operating on adevice communicates with one or more DHCP servers to obtainconfiguration information, including an IP address for the client's hostdevice. The configuration data is valid for a limited time interval,called a lease time. Before the lease expires at the end of the leasetime interval, the DHCP client may send a renew request message toextend the lease for some period of time, usually another or longerlease time.

1.0 Network Overview

FIG. 1 is a block diagram that illustrates a remote access network 100,according to an embodiment. A computer network is a geographicallydistributed collection of interconnected sub-networks (e.g.,sub-networks 110 a, 110 b, 110 c, 110 d collectively referencedhereinafter as sub-networks 110) for transporting data between nodes,such as computers, video content sources and television set boxes. Alocal area network (LAN) 110 a is an example of such a sub-network. Thenetwork's topology is defined by an arrangement of end nodes (e.g., endnodes 120 a, 120 b, 120 c, 120 d, 120 e, 120 f collectively referencedhereinafter as end nodes 120) that communicate with one another,typically through one or more intermediate network nodes, such as arouter or switch, that facilitate routing data between end nodes 120 ondifferent sub-networks. As used herein, an end node 120 is a node thatis configured to originate or terminate communications over the network.End nodes 120 include an Authentication, Authorization, Accounting (AAA)server host 120 e, and a DHCP server host 120 f.

In contrast, an intermediate network node facilitates the passage ofdata between end nodes. Intermediate network nodes depicted in FIG. 1include customer premises equipment (CPE) 150 a, 150 b, access modules152 a, 152 b, and Broadband Remote Access Server (BRAS) node 154.

Four sub-networks 110 that are typically involved in remote access aredepicted in FIG. 1. Each sub-network 110 may includes zero or moreintermediate network nodes. An IP network 110 d is the target for remoteaccess by users at a remote site 102.

To access IP network 110 d, a LAN 110 a is connected to CPE 150 a whichserves as a bridge to a network 110 b called the last mile network. Thelast mile network 110 b is built on a telephone wire infrastructure,such as dial-up or digital subscriber line (DSL), or cable televisioninfrastructure, either coaxial cable or optical fiber, or a wirelessinfrastructure, such as WiFi (IEEE standard 802.11). In an illustratedembodiment, LAN 110 a uses Ethernet infrastructure. Although the remotesite 102 includes an Ethernet LAN 110 a and two end nodes 120 a, 120 b,in other embodiments more or fewer end nodes 120 are connected to moreor fewer or different LANs 110, such as one or more LANs usingAsynchronous Transfer Mode (ATM) infrastructure. In some cases, CPE is atelephone modem using acoustic signals over a low-bandwidth legacytelephone system. In an illustrated embodiment, CPE 150 a is a digitalsubscriber line (DSL) modem for establishing a high bandwidth DSLconnection over the telephone wire as last mile network 110 b. In someembodiments, CPE 150 a is a combined router and end node, such as acable television set-top box.

Communications over last-mile network 110 b from CPE 150 a, 150 bterminate at access module 152 a. Although two CPEs 150 a, 150 b aredepicted connected to last-mile network 110 b, in other embodiments moreor fewer CPEs are connected to last-mile network 110 b. In anillustrated embodiment, access module 152 a is a DSL Access Module(DSLAM). In other embodiments, access module 152 a is a controller for abank of low-bandwidth modems or a cable or optical access module.

An internet service provider (ISP) typically maintains several accessmodules 152 a, 152 b and an access network 110 c for connection to theIP network 110 d (also called a “core” network) through a BroadbandRemote Access Server (BRAS) host 154. In many current embodiments, theaccess network 110 c is migrating to an Ethernet infrastructure thatsupports the Internet Protocol (IP).

According to an illustrated embodiment of the invention, a customer DHCPsession process 141 executes in a DHCP client at end node 120 a, and aprovider DHCP session process 142 executes in a BRAS on BRAS host 154.In various embodiments, another DHCP session process 143, 144 executesat AAA host 120 e or DHCP host 120 f, respectively, or some other nodeon IP network 110 d or access network 110 c, or some combination. TheDHCP session processes 141, 142, 143, 144 determine whether a node(e.g., end node 120 a) operating under a particular DHCP lease is stillcommunicating with one or more nodes on sub-networks 110.

2.0 Structural Elements

FIG. 2 is a block diagram that illustrates a generalized data packet 230communicated over a network, such as network 100. Each packet typicallycomprises one or more payloads of data, e.g. payloads 238, 248, eachencapsulated by at least one network header, e.g., headers 232, 242,respectively. For example, payloads are encapsulated by appending aheader before the payload, sometimes called prepending a header, andsometimes by appending a trailer (or tail) after the payload. Eachheader 232, 242 is formatted in accordance with a network communicationprotocol; header 232 is formatted according to a first protocol andheader 242 is formatted according to a second protocol. The header 242for the second protocol is included within the payload 238 of the firstprotocol. As used herein, a header for a particular protocol and itspayload constitute a data packet for that protocol and may also becalled a cell, frame, datagram or message for that protocol. In somepublications data packets for different protocols are distinguished inshorthand by using a different one of the above terms for differentprotocols, e.g., to refer to Ethernet frames and IP datagrams, but herethe terms are used interchangeably.

The header for a protocol typically includes type fields that identifythe protocol to which the header belongs and the next protocol in thepayload, if any. For example, the header 232 for the first protocolincludes type fields 236. The header for a protocol often includes adestination address or a source address, or both, for the information inthe payload. For example, the header 232 for the first protocol includesaddress fields 234 where the source and receiver address for the firstprotocol is located within the packet 230. As described above, atransmitted data packet's network headers include at least a physicallink (layer 1) header and a data-link (layer 2) header.

The physical (layer 1) header defines the electrical, mechanical andprocedural mechanisms for proper capture of the Ethernet frame, but isnot captured by a Media Access Controller. The layer 1 header mayinclude a DSL or ATM or Ethernet layer 1 header, or some combination.

The data-link header provides information for transmitting the packetover a particular physical link (i.e., a communication medium), such asa point-to-point link, Ethernet layer 2 link, wireless link, opticallink, etc. An intermediate network node typically contains multiplephysical links with multiple different nodes. To that end, the data-linkheader may specify a pair of “source” and “destination” networkinterfaces that are connected by the physical link. A network interfacecontains the mechanical, electrical and signaling circuitry and logicused to couple a network node to one or more physical links. A networkinterface is often associated with a hardware-specific address, known asa media access control (MAC) address. Accordingly, the source anddestination network interfaces in the data-link header are typicallyrepresented as source and destination MAC addresses. The data-linkheader may also store flow control, frame synchronization and errorchecking information used to manage data transmissions over the physicallink.

The internetwork header is a layer 3 header that provides informationdefining the source and destination address within the interconnectedsub-networks (internetwork). Notably, the path may span multiplephysical links. The internetwork header may be formatted according tothe Internet Protocol (IP), which specifies IP addresses of both asource and destination node at the end points of the logical path. Thus,the packet may “hop” from node to node along its logical path until itreaches the end node assigned to the destination IP address stored inthe packet's internetwork header. After each hop, the source anddestination MAC addresses in the packet's data-link header may beupdated, as necessary. However, the source and destination IP addressestypically remain unchanged as the packet is transferred from link tolink in the network.

DHCP is a control plane protocol that uses messages carried by the UserDatagram Protocol (UDP) to transmit IP addresses and other configurationinformation used to set up IP as the layer 3 protocol, i.e., theinternetwork protocol. UDP is a simple, small and fast layer 4 protocolwithout sophisticated error-tracking and sequencing mechanisms, whichutilizes IP broadcasts as a layer 3 protocol to carry UDP messages withDHCP payloads. IP broadcasts do not rely on individual IP addresses forrecipients, but direct data packets to all nodes on a particular networksegment. An IP broadcast is indicated by a special broadcast value inthe IP destination address field of an IP header. A host without an IPaddress, such as the DHCP client's host at startup, can send an IP datapacket by inserting a null address (e.g., 0.0.0.0) in the IP sourceaddress field of an IP header, and can receive IP broadcast datapackets. DHCP agents are processes on intermediate network nodes thatforward DHCP broadcasts received on one segment to a different networksegment, as desired.

FIG. 3 is a block diagram that illustrates a data packet 310 for a DHCPmessage communicated over a network. A DHCP message is carried inside aUDP payload 304 that follows the UDP header 302. The DHCP messageincludes a DHCP header 310 and a DHCP payload 320. According to the DHCPstandard, described in RFC 2131 and RFC 2132 the entire contents of eachof which are herby incorporated by reference as if fully set forthherein, the DHCP header 310 includes an op type field 312 and an xidfield 316. The DHCP header 310 also includes other fields that are notrelevant to understanding embodiments of the invention. Data held in theDHCP op type field 312 indicates whether the message is sent by a DHCPclient to a DHCP server, or is sent by a DHCP server to a DHCP client,as is well known in the art. Data held in the DHCP xid field 312 isusually used by a DHCP client to match incoming DHCP messages withpending DHCP requests for configuration data.

The DHCP payload 320 includes one or more required or optional fields,or both, depending on the message type indicated in a message typefield. A DHCP option field 322 is illustrated. The DHCP option field 322includes an option type field 323 and option length field 324 and one ormore data fields 326, depending on the option type expressed in theoption type field 323. Data held in the option type field 323 indicatesthe type of option. Data held in the DHCP option length field 324indicates the length of the DHCP option. Data held in the DHCP optiondata fields 326 indicates the values of one or more attributesassociated with the option type indicated in the option type field 323.One option carried in the DHCP payload contains an attribute thatindicates the type of the DHCP message, such as a DHCPDISCOVER messageor a DHCPOFFER message. Different values in the attribute fieldcorrespond to different message types. All of the message types aredefined in RFC 2131, RFC 2132 and subsequent RFCs, well known in theart. A DHCP payload may carry multiple data options fields like field322.

FIG. 4 is a block diagram that illustrates a user end node host 420,according an embodiment. User end node host 420 includes a modified DHCPclient 422 and a customer DHCP session process 424, such as process 141on end node 120 a. In the illustrated embodiment, the modified DHCPclient 422 has an Application Program Interface (API) through whichexternal processes can exchange information with the modified DHCPclient 422. In some embodiments, the customer DHCP session process 424is incorporated within the modified DHCP client 422.

According to embodiments of the invention, the modified DHCP client 422is modified from the standard DHCP client in order to engage thecustomer DHCP session process 424 to accomplish session keep-alive andtermination using DHCP messages, as described in more detail below withreference to FIG. 6. Such a modified DHCP client allows PPP sessionfunctionality to be omitted.

FIG. 5 is a block diagram that illustrates a BRAS host 550, according toan embodiment. The BRAS host 550 includes a modified BRAS 552, amodified DHCP server 560 and a provider DHCP session process 562, suchas process 142 on BRAS host 154. The modified DHCP server 560 ismodified from a standard DHCP server in order to engage provider DHCPsession process 562.

In other embodiments provider DHCP session process 562 is external tomodified BRAS 552 and interacts with modified BRAS 552 through an API.In some embodiments, the modified DHCP server 560 is omitted. In someembodiments, a DHCP relay agent is included in the modified BRAS 552.According to some embodiments of the invention, the modified BRAS 552 ismodified in order to directly or indirectly engage the provider DHCPsession process 562 to accomplish session keep-alive and terminationusing DHCP messages, as described in more detail below with reference toFIG. 6. In the illustrated embodiment, the modified BRAS 552 engages theprovider DHCP session process 562 indirectly though a modified DHCPserver 560 that itself is modified to engage the provider DHCP sessionprocess 562

In some embodiments, the provider DHCP session process 562 is engaged,directly or indirectly by a DHCP server on a different host from theBRAS host, such as on DHCP host 120 f, as indicated by process 144. Insome embodiments, the provider DHCP session process 562 is engaged,directly or indirectly by a different server on a different host fromthe BRAS host, such as on AAA host 120 e, as indicated by process 143.

3.0 Methods for Ip Sessions Using DHCP

According to various embodiments of the invention, DHCP standards areadapted to allow DHCP messages to support session keep-alive andtermination, such as provided by PPP. Any authentication required for auser to begin communication over the network has occurred before themethod described here. In some embodiments, the authentication isperformed using PPP. In some embodiments, the authentication isperformed using another protocol. In some embodiments, theauthentication is performed using DHCP as described in Townsley. In someembodiments, no authentication is performed.

According to an illustrated embodiment of the invention, two new DHCPmessage types are defined:

1—DHCP-ECHOREQUEST

2—DHCP-ECHOREPLY

to support a new session keep-alive and termination functionality withinDHCP.

The DHCPAUTH messages follow the format for DHCP messages defined in RFC2131. These new messages are identified by the presence of a DHCPMessage Type option 322, which encodes DHCP message types. For example,one value in DHCP Message Type option field 322 is associated with aDHCP-ECHOREQUEST message type; and a second value in DHCP Message Typeoption field 322 is associated with a DHCP-ECHOREPLY message type. TheDHCP standard should be updated to allow this association. Other fieldsin the DHCP message header, such as siaddr andfname, are left unused. Invarious other embodiments, one or more other fields in the DHCP header(such as the xid field 316) or payload are used to indicate these typesof messages in addition to or instead of the fields used in theillustrated embodiment.

In the illustrated embodiment, the data in a DHCP-ECHOREQUEST andDHCP-ECHOREPLY message is carried within an option field, for example,as option field 322. As stated above, the option type field 323indicates whether the message is a request or a reply. The option lengthfield 324 holds data that indicates the length of the data fields 326 asa number of octets (an octet is eight binary digits called bits). Forexample, the option type field 323 is eight bits, the option lengthfield 324 is eight bits, and the data fields 326 are the next number ofoctets indicated by the value in the option length field 324. In theillustrated embodiment the data in the option length field 324 indicatesa length of one (1) octet.

The data fields 326 are zero or more octets carrying the data specificfor the option type. In the illustrated embodiment, the one octet ofdata fields 326 holds data that indicates whether the message is sentfrom a DHCP client or a DHCP server. This information is used to preventloop-back situations, e.g., situations in which the request received wasactually issued by the same DHCP process. In an illustrated embodiment asingle bit of the octet in data fields 326, called a “C-bit,” is used.For example, a value of “1” in the C-bit indicates the message is sentfrom a modified DHCP client. A value of “0” in the C-bit indicates themessage is sent from a modified DHCP server.

In these embodiments, any DHCP-ECHOREQUEST message that is received isanswered with a DHCP-ECHOREPLY message. As a result, a first process,such as a modified BRAS, can determine whether a second process engagedin IP unicast communications over the IP network (such as end node 120a) is still active by sending a DHCP-ECHOREQUEST and receiving acorresponding DHCP-ECHOREPLY within an appropriate time. If thecorresponding reply is not received within an appropriate time, thenactions appropriate for loss of communication can be taken, such asterminating billing or attempting to re-establish connection. Thecorresponding reply can be distinguished based on a value in the xidfield, as is done currently for correlating DHCP OFFER response messagewith a DHCP DISCOVER request message.

3.1 DHCP Session Process

FIG. 6 is a flow diagram that illustrates a method 600 at a DHCP sessionprocess, such as process 424 in user end node 420 and process 562 inBRAS host 550, according to an embodiment. Although steps are shown inFIG. 6 in a particular order for purposes of illustration, in otherembodiments the steps may be performed in a different order oroverlapping in time or one or more steps may be omitted or the steps maybe changed in some combination of ways. In some embodiments, the stepsdepicted in FIG. 6 are included in both customer DHCP session process424 and provider DHCP session process 562, but the implementations ofthe steps differ between the two processes.

In step 610, a DHCP lease is established for configuration data forcustomer premises equipment. For example, after authentication, a leaseis offered to modified DHCP client 422 on host 120 a for an IP addressand other configuration data and accepted by the client 422. On modifiedBRAS host 550, the acceptance from client 422 is received by modifiedDHCP server.

In step 620, it is determined whether conditions are satisfied fortesting a connection state between the modified DHCP client 422 and themodified BRAS 552. For example, in some embodiments, at the client 422on end node 120 a it is determined that a request sent over IP network110 d to a server on end node 120 c has not resulted in a response fromend node 120 c after one or more retransmits. In some embodiments it isdetermined at client 422 that no data packets have been received fromBRAS 552 on host 154 for a particular time associated with a keep-alivetest interval. In some embodiments it is determined at the BRAS 552 422on host 154 that no data packets have been received from end node 120 afor a particular time associated with a keep-alive test interval. Inother embodiments one or more other conditions are used to determinethat connection test should be tested. If it is determined in step 620that conditions are not satisfied for testing the connection state, thencontrol passes to step 630.

In step 630, unicast IP communications between customer node and nodeson IP network (e.g., IP network 110 d) continue across access network(e.g., across access network 110 c).

If it is determined in step 620 that conditions are satisfied fortesting the connection state, then control passes to step 624. In step624, the DHCP session process on the local node sends a DHCP echorequest, such as a DHCP-ECHOREQUEST message. For example, in a modifiedDHCP server 560, a DHCP-ECHOREQUEST with a “0” in the C-bit is unicastto the customer node. In a modified DHCP client 422, a DHCP-ECHOREQUESTwith a “1” in the C-bit is unicast to the provider node. In anillustrated embodiment, a unique value is placed in the xid field 316 ofthe DHCP header so that an echo reply to this request can bedistinguished from other echo reply messages that may be received. Insome embodiments a reply timer is started to determine the time spentwaiting for a valid echo reply.

In the illustrated embodiment, control passes from step 624 to step 630to continue IP unicast communications until the request goes unansweredwith a predetermined reply time interval. In some embodiments, the DHCPsession process goes into a wait mode and does not continue IP unicastcommunications until the request is answered with a valid DHCP echoreply within the reply time, as described below in steps 670 and 674. Insuch embodiments, control passes from step 624 to step 670.

In step 640, it is determined whether a DHCP lease for communicationsbetween the customer node and nodes on the IP network expires. If so,control passes to step 642. In step 642 it is determined whether theDHCP client on the customer node requests a lease renewal in time. Ifso, control passes back to step 610 to establish a lease for suchcommunications. For example, as a lease time interval is about toexpire, a DHCP client process on customer node (e.g., end node 120 a)sends a DHCP renewal message to a DHCP server (e.g., modified DHCPserver 560 on BRAS host 550. If in step 642 it is determined that theDHCP client on the customer node does not request a lease renewal intime, then control passes to step 690. In step 690 the lease expires andunicast IP communications between the customer node and nodes on the IPnetwork cease.

If in step 640 it is determined that a DHCP lease for communicationsbetween the customer node and nodes on the IP network does not expire,then control passes to step 650. In some embodiments, step 640 isomitted and control passes directly to step 650.

In step 650 it is determined whether a DHCP echo request is receivedamong the unicast IP data packets. If so, control passes to step 652.

In step 652, it is determined whether the echo request is valid. In someembodiments in which step 640 is omitted, step 652 includes determiningwhether there is DHCP lease in effect for communications between thecustomer node and nodes on the IP network. In some embodiments, step 652includes determining whether the request is not a loop-back request. Forexample, it is determined during step 652 that the DHCP process (e.g., aDHCP client or DHCP serer) that sent the request, as indicated in theillustrated embodiment by the C-bit in data fields 326 of aDHCP-ECHOREQUEST message, is different from the DHCP process receivingthe request. If the echo request is not valid, it is ignored; andcontrol passes back to step 620. If the echo request is valid, controlpasses to step 660 to reply. In some embodiments, step 652 is omittedand control passes directly to step 660.

In step 660 a DHCP echo reply message is returned, i.e., the DHCPsession process on the local node sends a DHCP echo reply, such as aDHCP-ECHOREPLY message. For example, in a modified DHCP server 560, aDHCP-ECHOREPLY with a “0” in the C-bit is unicast to the customer node.In a modified DHCP client 422, a DHCP-ECHOREPLY with a “1” in the C-bitis unicast to the provider node. In an illustrated embodiment, theunique value from the xid field 316 of the DHCP-ECHOREQUEST message isplaced in the xid field 316 of the DHCP header of the DHCP-ECHOREPLYmessage so that this reply can be associated with the request. Controlthen passes back to step 620.

If it is determined in step 650 that a DHCP echo request is not receivedamong the unicast IP data packets, then control passes to step 670. Instep 670, it is determined whether a message received is a valid DHCPecho reply. In some embodiments, any DHCP echo reply is considered avalid DHCP echo reply. In an illustrated embodiment, only a DHCP echoreply in response to a DHCP echo request sent by the local node can be avalid reply. If the local node sent no DHCP echo request, e.g., did notexecute step 624, then no DHCP echo reply is a valid reply.

If the local node did send an echo request in step 624, then, in somesuch embodiments, the echo reply must correspond to the request to bevalid. In the illustrated embodiments, the correspondence is determinedif the values in the xid field of the reply matches a value in an xidfield of any request sent during step 624. In some embodiments, a listof outstanding echo request messages sent by the local node andassociated xid values are maintained at the local node Therefore a replyto a request sent by another node, e.g., with an xid value not on thelist maintained at the local node, is determined during step 670 of suchembodiments to be an invalid echo reply.

To prevent a loop-back reply from being mistaken as a valid echo reply,in some embodiments, step 670 includes determining whether the reply wassent from a different DHCP process than at the local node. For example,if the local node is the modified BRAS with a modified DHCP server, thena DHCP-ECHOREPLY message with a C-bit of “0”(indicating the reply wassent by a DHCP server) is determined to be an invalid echo reply.Similarly, if the local node is the modified DHCP client, then aDHCP-ECHOREPLY message with a C-bit of “1” (indicating the reply wassent by a DHCP client) is determined to be an invalid echo reply.

If the valid DHCP echo reply message is not received in step 670, thencontrol passes to step 674. In step 674, it is determined whether thetime for a valid reply has expired. For example, it is determinedwhether the reply timer set during step 624 has exceeded a predeterminedmaximum reply time interval.

If it is determined in step 674 that the time for a valid reply has notexpired, then the unicast communication can be processed normally, andcontrol passes to step 688 to do so. Any processing of IP data packetsknown in the art may be performed at the local node during step 688.Control then passes back to step 620 to see if new conditions fortesting the connection have been satisfied and, if not, continue IPunicasts in step 630.

However, if it is determined in step 674 that the time for a valid replyhas expired, then the local node should respond to a loss of theconnection between the customer node and the IP network; and controlpasses to step 680.

In step 680, the local node responds to the loss of connection. Anyresponse may be performed. For example, in some embodiments in which thelocal node executes a DHCP server, the resources allocated to thecustomer node are reclaimed earlier than allowed by the DHCP lease. Insome embodiments the local node attempts to authenticate the customernode. In some embodiments, a billing agent process is notified that thecustomer session has ended and to cease charges based on connect-time.In some embodiments in which the local node executes a DHCP client, theclient attempts to commence access, such as by sending a new DHCPDISCOVER message, or again logging onto the network in any conventionalway. In embodiments that implement one or more methods of Townsley, theDHCP client again responds to a DHCP challenge issued by a challengingprocess at the BRAS or DHCP server or AAA server. In some embodiments,the customer node releases the local resources allocated to thecommunication session.

If it is determined in step 670 that a message received is a valid echoreply, then control passes to step 672 to keep the session going. Ineffect, receipt of the valid echo reply has the effect of receiving asession keep-alive message. Any method may be used in step 672 to keepthe session alive. In step 672 for the illustrated embodiment, akeep-alive timer for tracking time since a last keep-alive message isreset; and the timer started in step 624 to mark time elapsed since anecho request was sent is stopped.

Using the method 600, DHCP messages are utilized to determine when tokeep-alive an IP session and when to terminate the session. Thisreplaces similar functionality currently provided by PPP. Therefore, insome embodiments, PPP session maintenance functions are not utilized. Insome of these embodiments, PPP authentication functions are also notutilized but instead replaced by the DHCP authentication functions ofTownsley.

The method 600 does not suffer the disadvantage of a short DHCP leasetime used in a prior approach. For example, the short DHCP lease timesof a few seconds require the BRAS and DHCP client on the customer nodeto generate and process large DHCP messages every few seconds for everyactive IP session.

The method 600 does not suffer the disadvantage of using ARP to detect aloss of connection. Because the method involves direct unicastcommunication between the DHCP client and the modified BRAS, amis-configured or rogue node is not likely to be able to respond to theDHCP echo request.

3.2 Enhanced Security

Unlike a basic PPP exchange, DHCP packets including DHCP-ECHOREQUEST andDHCP-ECHOREPLY messages may be freely routed by IP routers acrossmultiple hops.

In some embodiments, an echo request is only considered valid if ittraverses only one network segment (i.e., passes through no interveningintermediate network nodes). This prevents malicious IP users on IPnetwork 110 d from issuing valid echo requests. In some of theseembodiments, the single segment requirement is enforced using the IPTime-to-Live (TTL) field, which is set by the originator of a messageand decremented by each intermediate network node. The maximum value forthis field is 255. Thus an echo request can be assured to be issued onthe same segment if the requesting process inserts a value of 255 in theTTL field and the echo request arrives with the value 255 in that field.In such embodiments, step 652 includes determining whether the TTL fieldof the received challenge is equal to 255.

This method can also be combined with a modification to a DHCP relayagent on access network 110 c that restricts the relay agent fromforwarding DHCP-ECHOREQUEST messages from external DHCP servers, whichensures that any DHCP-ECHOREQUEST messages received by the DHCP clientwere originated in the BRAS.

In some embodiments, a DHCP authentication challenge is considered validonly if it is the first received after a lease is granted by a DHCPserver, as depicted in the illustrated embodiment. In some suchembodiments, after a lease is granted, the customer DHCP session processis put in a echo-enabled state. When in the echo-enabled state, theclient determines during step 652 that a DHCP echo request message sentto it is valid if it satisfies other criteria for validity describedabove. The customer DHCP session process is put in an echo-disabledstate after a DHCP lease expires and before a DHCP lease is obtained. Insuch an echo-disabled state, the customer DHCP session processdetermines during step 652 that any DHCP echo request message sent to itis not valid.

In some embodiments, a DHCP echo-request message is considered validonly if received at a reasonable rate less than some rate limit. In somesuch embodiments, after an echo request, the customer DHCP sessionprocess is put in an echo-disabled state. When in the echo-disabledstate, the customer DHCP session process determines during step 652 thatany DHCP echo request message sent to it is not valid. The customer DHCPsession process is put in an echo-enabled state after a time based onthe rate limit. In such an echo-enabled state, the customer DHCP sessionprocess determines during step 652 that a DHCP echo request message sentto it is valid if it satisfies other criteria for validity describedabove.

In some embodiments a hash function is used with a shared secret and ahash value included in the echo request to determine whether the requestis valid in step 652. In some embodiments a hash function is used with ashared secret and a hash value included in the echo reply to determinewhether the reply is valid in step 670.

4.0 Implementation Mechanisms—Hardware Overview

FIG. 7 is a block diagram that illustrates a computer system 700 uponwhich an embodiment of the invention may be implemented. The preferredembodiment is implemented using one or more computer programs running ona network node such as a router device. Thus, in this embodiment, thecomputer system 700 is a network node.

Computer system 700 includes a communication mechanism such as a bus 710for passing information between other internal and external componentsof the computer system 700. Information is represented as physicalsignals of a measurable phenomenon, typically electric voltages, butincluding, in other embodiments, such phenomena as magnetic,electromagnetic, pressure, chemical, molecular atomic and quantuminteractions. For example, north and south magnetic fields, or a zeroand non-zero electric voltage, represent two states (0, 1) of a binarydigit (bit). A sequence of binary digits constitutes digital data thatis used to represent a number or code for a character. A bus 710includes many parallel conductors of information so that information istransferred quickly among devices coupled to the bus 710. One or moreprocessors 702 for processing information are coupled with the bus 710.A processor 702 performs a set of operations on information. The set ofoperations include bringing information in from the bus 710 and placinginformation on the bus 710. The set of operations also typically includecomparing two or more units of information, shifting positions of unitsof information, and combining two or more units of information, such asby addition or multiplication. A sequence of operations to be executedby the processor 702 constitute computer instructions.

Computer system 700 also includes a memory 704 coupled to bus 710. Thememory 704, such as a random access memory (RAM) or other dynamicstorage device, stores information including computer instructions.Dynamic memory allows information stored therein to be changed by thecomputer system 700. RAM allows a unit of information stored at alocation called a memory address to be stored and retrievedindependently of information at neighboring addresses. The memory 704 isalso used by the processor 702 to store temporary values duringexecution of computer instructions. The computer system 700 alsoincludes a read only memory (ROM) 706 or other static storage devicecoupled to the bus 710 for storing static information, includinginstructions, that is not changed by the computer system 700. Alsocoupled to bus 710 is a non-volatile (persistent) storage device 708,such as a magnetic disk or optical disk, for storing information,including instructions, that persists even when the computer system 700is turned off or otherwise loses power.

The term computer-readable medium is used herein to refer to any mediumthat participates in providing information to processor 702, includinginstructions for execution.

Such a medium may take many forms, including, but not limited to,non-volatile media, volatile media and transmission media. Non-volatilemedia include, for example, optical or magnetic disks, such as storagedevice 708. Volatile media include, for example, dynamic memory 704.Transmission media include, for example, coaxial cables, copper wire,fiber optic cables, and waves that travel through space without wires orcables, such as acoustic waves and electromagnetic waves, includingradio, optical and infrared waves. Signals that are transmitted overtransmission media are herein called carrier waves.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, a hard disk, a magnetic tape or any othermagnetic medium, a compact disk ROM (CD-ROM), a digital video disk (DVD)or any other optical medium, punch cards, paper tape, or any otherphysical medium with patterns of holes, a RAM, a programmable ROM(PROM), an erasable PROM (EPROM), a FLASH-EPROM, or any other memorychip or cartridge, a carrier wave, or any other medium from which acomputer can read.

Information, including instructions, is provided to the bus 710 for useby the processor from an external terminal 712, such as a terminal witha keyboard containing alphanumeric keys operated by a human user, or asensor. A sensor detects conditions in its vicinity and transforms thosedetections into signals compatible with the signals used to representinformation in computer system 700. Other external components ofterminal 712 coupled to bus 710, used primarily for interacting withhumans, include a display device, such as a cathode ray tube (CRT) or aliquid crystal display (LCD) or a plasma screen, for presenting images,and a pointing device, such as a mouse or a trackball or cursordirection keys, for controlling a position of a small cursor imagepresented on the display and issuing commands associated with graphicalelements presented on the display of terminal 712. In some embodiments,terminal 712 is omitted.

Computer system 700 also includes one or more instances of acommunications interface 770 coupled to bus 710. Communication interface770 provides a two-way communication coupling to a variety of externaldevices that operate with their own processors, such as printers,scanners, external disks, and terminal 712. Firmware or software runningin the computer system 700 provides a terminal interface orcharacter-based command interface so that external commands can be givento the computer system. For example, communication interface 770 may bea parallel port or a serial port such as an RS-232 or RS-422 interface,or a universal serial bus (USB) port on a personal computer. In someembodiments, communications interface 770 is an integrated servicesdigital network (ISDN) card or a digital subscriber line (DSL) card or atelephone modem that provides an information communication connection toa corresponding type of telephone line. In some embodiments, acommunication interface 770 is a cable modem that converts signals onbus 710 into signals for a communication connection over a coaxial cableor into optical signals for a communication connection over a fiberoptic cable. As another example, communications interface 770 may be alocal area network (LAN) card to provide a data communication connectionto a compatible LAN, such as Ethernet. Wireless links may also beimplemented. For wireless links, the communications interface 770 sendsand receives electrical, acoustic or electromagnetic signals, includinginfrared and optical signals, which carry information streams, such asdigital data. Such signals are examples of carrier waves

In the illustrated embodiment, special purpose hardware, such as anapplication specific integrated circuit (IC) 720, is coupled to bus 710.The special purpose hardware is configured to perform operations notperformed by processor 702 quickly enough for special purposes. Examplesof application specific ICs include graphics accelerator cards forgenerating images for display, cryptographic boards for encrypting anddecrypting messages sent over a network, speech recognition, andinterfaces to special external devices, such as robotic arms and medicalscanning equipment that repeatedly perform some complex sequence ofoperations that are more efficiently implemented in hardware.

In the illustrated computer used as a router, the computer system 700includes switching system 730 as special purpose hardware for switchinginformation for flow over a network. Switching system 730 typicallyincludes multiple communications interfaces, such as communicationsinterface 770, for coupling to multiple other devices. In general, eachcoupling is with a network link 732 that is connected to another devicein or attached to a network, such as local network 780 in theillustrated embodiment, to which a variety of external devices withtheir own processors are connected. In some embodiments an inputinterface or an output interface or both are linked to each of one ormore external network elements. Although three network links 732 a, 732b, 732 c are included in network links 732 in the illustratedembodiment, in other embodiments, more or fewer links are connected toswitching system 730. Network links 732 typically provides informationcommunication through one or more networks to other devices that use orprocess the information. For example, network link 732 b may provide aconnection through local network 780 to a host computer 782 or toequipment 784 operated by an Internet Service Provider (ISP). ISPequipment 784 in turn provides data communication services through thepublic, world-wide packet-switching communication network of networksnow commonly referred to as the Internet 790. A computer called a server792 connected to the Internet provides a service in response toinformation received over the Internet. For example, server 792 providesrouting information for use with switching system 730.

The switching system 730 includes logic and circuitry configured toperform switching functions associated with passing information amongelements of network 780, including passing information received alongone network link, e.g. 732 a, as output on the same or different networklink, e.g., 732 c. The switching system 730 switches information trafficarriving on an input interface to an output interface according topre-determined protocols and conventions that are well known. In someembodiments, switching system 730 includes its own processor and memoryto perform some of the switching functions in software. In someembodiments, switching system 730 relies on processor 702, memory 704,ROM 706, storage 708, or some combination, to perform one or moreswitching functions in software. For example, switching system 730, incooperation with processor 704 implementing a particular protocol, candetermine a destination of a packet of data arriving on input interfaceon link 732 a and send it to the correct destination using outputinterface on link 732 c. The destinations may include host 782, server792, other terminal devices connected to local network 780 or Internet790, or other routing and switching devices in local network 780 orInternet 790.

The invention is related to the use of computer system 700 forimplementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 700 in response to processor 702 executing one or more sequencesof one or more instructions contained in memory 704. Such instructions,also called software and program code, may be read into memory 704 fromanother computer-readable medium such as storage device 708. Executionof the sequences of instructions contained in memory 704 causesprocessor 702 to perform the method steps described herein. Inalternative embodiments, hardware, such as application specificintegrated circuit 720 and circuits in switching system 730, may be usedin place of or in combination with software to implement the invention.Thus, embodiments of the invention are not limited to any specificcombination of hardware and software.

The signals transmitted over network link 732 and other networks throughcommunications interfaces such as interface 770, which carry informationto and from computer system 700, are exemplary forms of carrier waves.Computer system 700 can send and receive information, including programcode, through the networks 780, 790 among others, through network links732 and communications interfaces such as interface 770. In an exampleusing the Internet 790, a server 792 transmits program code for aparticular application, requested by a message sent from computer 700,through Internet 790, ISP equipment 784, local network 780 and networklink 732 b through communications interface in switching system 730. Thereceived code may be executed by processor 702 or switching system 730as it is received, or may be stored in storage device 708 or othernon-volatile storage for later execution, or both. In this manner,computer system 700 may obtain application program code in the form of acarrier wave.

Various forms of computer readable media may be involved in carrying oneor more sequence of instructions or data or both to processor 702 forexecution. For example, instructions and data may initially be carriedon a magnetic disk of a remote computer such as host 782. The remotecomputer loads the instructions and data into its dynamic memory andsends the instructions and data over a telephone line using a modem. Amodem local to the computer system 700 receives the instructions anddata on a telephone line and uses an infra-red transmitter to convertthe instructions and data to an infra-red signal, a carrier wave servingas the network link 732 b. An infrared detector serving ascommunications interface in switching system 730 receives theinstructions and data carried in the infrared signal and placesinformation representing the instructions and data onto bus 710. Bus 710carries the information to memory 704 from which processor 702 retrievesand executes the instructions using some of the data sent with theinstructions. The instructions and data received in memory 704 mayoptionally be stored on storage device 708, either before or afterexecution by the processor 702 or switching system 730.

5.0 Extensions and Alternatives

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

1. A method for supporting subscriber sessions for access to a serviceprovider network: receiving from a first node of a provider network nodeand a customer network node, at a different second node of the providernetwork node and the customer network node, a Dynamic Host ConfigurationProtocol (DHCP) formatted echo-request message that includes a DHCPoption field that holds data that indicates an echo-request type; and inresponse to receiving the echo-request message, sending to the firstnode a DHCP formatted echo-reply message that corresponds to theecho-request message, wherein the echo-reply message includes a DHCPoption field that holds data that indicates an echo-reply type, whichwhen received by the first node causes the first node to determine aconnected state with the second node.
 2. A method as recited in claim 1,wherein the provider network node is on premises of a service providerfor an Internet Protocol (IP) network and a customer network node is onpremises of a customer different from the premises of the provider.
 3. Amethod as recited in claim 1, wherein said provider network nodeexecutes a gateway server for remote access to the IP network.
 4. Amethod as recited in claim 1, wherein said customer network nodeexecutes a client for remote access to the IP network.
 5. A method asrecited in claim 1, said step of sending the echo-reply message furthercomprising placing data from a DHCP header xid field of the echo-requestmessage into a DHCP header xid field of the echo-reply message, wherebythe echo-reply message corresponds to the echo-request message.
 6. Amethod as recited in claim 1, wherein: the method further comprisesdetermining whether the echo-request message is valid; and said step ofsending the echo-reply message is performed only if it is determinedthat the echo-request message is valid.
 7. A method as recited in claim6, said step of determining whether the echo-request message is validfurther comprises determining whether a DHCP lease is in effect forconfiguration data for unicast communications between the providernetwork node and the customer network node.
 8. A method as recited inclaim 6, wherein: the method is performed by a local DHCP process of aDHCP server process and a DHCP client process; said step of receivingthe echo-request message further comprises receiving the echo-requestmessage that includes the DHCP option field that holds sender data thatindicates a sending DHCP process of a DHCP server process and a DHCPclient process, which sending DHCP process originated the echo-requestmessage; and said step determining whether the echo-request message isvalid further comprises determining whether the echo-request is not aloop back request by determining whether the sending DHCP process isdifferent from the local DHCP process.
 9. A method as recited in claim8, said step of sending the echo-reply message further comprisingsending the echo-reply message that includes the DHCP option field thatholds sender data that indicates whether the local DHCP process is aDHCP server or a DHCP client.
 10. A method as recited in claim 1,wherein a Point to Point Protocol (PPP) is not used to determineconnection state between the first node and the second node.
 11. Amethod for supporting subscriber sessions for access to a serviceprovider network: determining whether conditions are satisfied fortesting connection state between a provider network node on an InternetProtocol (IP) network and a customer network node; if conditions aresatisfied for testing connection state, then sending, from a first nodeof the provider network node and the customer network node to adifferent second node of the provider network node and the customernetwork node, a Dynamic Host Configuration Protocol (DHCP) formattedecho-request message that includes an option field that holds data thatindicates an echo-request type, which when received by the second nodecauses the second node to return a DHCP formatted echo-reply messagethat includes an option field that holds data that indicates anecho-reply type; determining whether an echo-reply message thatcorresponds to the echo-request message is received within a particularreply time interval after sending the echo-request message; and if it isdetermined that the echo-reply message that corresponds to theecho-request message is not received within the particular reply timeinterval, then responding to a loss of connection state between theprovider network node and the customer network node.
 12. A method asrecited in claim 11, wherein the provider network node is on premises ofa service provider for the Internet Protocol (IP) network and a customernetwork node is on premises of a customer different from the premises ofthe provider.
 13. A method as recited in claim 11, wherein said providernetwork node executes a gateway server for remote access to the IPnetwork.
 14. A method as recited in claim 11, wherein said customernetwork node executes a client for remote access to the IP network. 15.A method as recited in claim 11, said step of determining whether theecho-reply message corresponds to the echo-request message furthercomprising determining whether first data in a DHCP header xid field ofthe echo-reply message matches second data in a DHCP header xid field ofthe echo-request message.
 16. A method as recited in claim 11, said stepof sending the echo-request message further comprising sending anecho-request message that includes in the option field sender type datathat indicates whether the method is performed by a DHCP client or aDHCP server.
 17. A method as recited in claim 16, said step ofdetermining whether the echo-reply message corresponds to theecho-request message further comprising determining whether the sendertype data in the echo-reply message is different from the sender typedata in the echo request message
 18. A method as recited in claim 11,said step of determining whether conditions are satisfied for testingconnection state further comprising determining whether no data packetsare received at a remote access server on the provider network node fromthe customer network node within a particular keep-alive time interval.19. A method as recited in claim 11, said step of determining whetherconditions are satisfied for testing connection state further comprisingdetermining whether a DHCP lease is in effect for configuration data forunicast communications with the customer network node.
 20. A method asrecited in claim 11, said step of determining whether conditions aresatisfied for testing connection state further comprising determiningwhether no data packets are received at a customer network node from aremote access server on the provider network node within a particularkeep-alive time interval.
 21. A method as recited in claim 11, said stepof responding to a loss of connection state further comprisingattempting to re-establish a connection state between the providernetwork node and the customer network node.
 22. A method as recited inclaim 11, said step of responding to a loss of connection state furthercomprising notifying a billing agent process of termination of a sessionbetween the customer network node and the provider network node.
 23. Amethod as recited in claim 11, wherein a Point to Point Protocol (PPP)is not used for testing connection state between the provider networknode and the customer network node.
 24. An apparatus for supportingsubscriber sessions with a service provider network, comprising: meansfor receiving from a first node of a provider network node and acustomer network node, at a different second node of the providernetwork node and the customer network node, a Dynamic Host ConfigurationProtocol (DHCP) formatted echo-request message that includes a DHCPoption field that holds data that indicates an echo-request type; andmeans for sending to the first node a DHCP formatted echo-reply messagethat corresponds to the echo-request message in response to receivingthe echo-request message, wherein the echo-reply message includes a DHCPoption field that holds data that indicates an echo-reply type, whichwhen received by the first node causes the first node to determine aconnected state with the second node.
 25. An apparatus for supportingsubscriber sessions with a service provider network, comprising: meansfor determining whether conditions are satisfied for testing connectionstate between a provider network node on an Internet Protocol (IP)network and a customer network node; means for sending from a first nodeof the provider network node and the customer network node to adifferent second node of the provider network node and the customernetwork node, a Dynamic Host Configuration Protocol (DHCP) formattedecho-request message that includes an option field that holds data thatindicates an echo-request type, if conditions are satisfied for testingconnection state, wherein when the echo-request message is received bythe second node the echo-request message causes the second node toreturn a DHCP formatted echo-reply message that includes an option fieldthat holds data that indicates an echo-reply type; means for determiningwhether an echo-reply message that corresponds to the echo-requestmessage is received within a particular reply time interval aftersending the echo-request message; and means for responding to a loss ofconnection state between the provider network node and the customernetwork node, if it is determined that the echo-reply message thatcorresponds to the echo-request message is not received within theparticular reply time interval.
 26. An apparatus for supportingsubscriber sessions with a service provider network, comprising: anetwork interface that is coupled to a network for communicating one ormore packet flows therewith; one or more processors; a computer readablemedium; and one or more sequences of instructions stored on the computerreadable medium, which, when executed by the one or more processors,causes the one or more processors to carry out the steps of: receivingfrom a network node a Dynamic Host Configuration Protocol (DHCP)formatted echo-request message that includes a DHCP option field thatholds data that indicates an echo-request type; and in response toreceiving the echo-request message, sending to the network node a DHCPformatted echo-reply message that corresponds to the echo-requestmessage, wherein the echo-reply message includes a DHCP option fieldthat holds data that indicates an echo-reply type, which when receivedby the network node causes the first node to determine a connected statewith the second node.
 27. An apparatus as recited in claim 26, whereinthe apparatus is one of a provider network node on premises of a serviceprovider for an Internet Protocol (IP) network and a customer networknode on premises of a customer different from the premises of theprovider; and the network node is a different one of the providernetwork node and the customer network node.
 28. An apparatus as recitedin claim 27, wherein said provider network node executes a gatewayserver for remote access to the IP network.
 29. An apparatus as recitedin claim 27, wherein said customer network node executes a client forremote access to the IP network.
 30. An apparatus as recited in claim26, said step of sending the echo-reply message further comprisingplacing data from a DHCP header xid field of the echo-request messageinto a DHCP header xid field of the echo-reply message, whereby theecho-reply message corresponds to the echo-request message.
 31. Anapparatus as recited in claim 26, wherein: execution of the one or moresequences of instructions further causes the one or more processors tocarry out the step of determining whether the echo-request message isvalid; and said step of sending the echo-reply message is performed onlyif it is determined that the echo-request message is valid.
 32. Anapparatus as recited in claim 31, said step of determining whether theecho-request message is valid further comprises determining whether aDHCP lease is in effect for configuration data for unicastcommunications between the apparatus and the network node.
 33. Anapparatus as recited in claim 31, wherein: execution of the one or moresequences of instructions further causes the one or more processors tocarry out the steps of a local DHCP process of a DHCP server process anda DHCP client process; said step of receiving the echo-request messagefurther comprises receiving the echo-request message that includes theDHCP option field that holds sender data that indicates a sending DHCPprocess of a DHCP server process and a DHCP client process, whichsending DHCP process originated the echo-request message; and said stepdetermining whether the echo-request message is valid further comprisesdetermining whether the echo-request is not a loop back request bydetermining whether the sending DHCP process is different from the localDHCP process.
 34. An apparatus as recited in claim 33, said step ofsending the echo-reply message further comprising sending the echo-replymessage that includes the DHCP option field that holds sender data thatindicates the local DHCP process.
 35. An apparatus as recited in claim26, wherein a Point to Point Protocol (PPP) is not used to determineconnection state between the first node and the second node.
 36. Anapparatus for supporting subscriber sessions with a service providernetwork, comprising: a network interface that is coupled to a networkfor communicating one or more packet flows therewith; one or moreprocessors; a computer readable medium; and one or more sequences ofinstructions stored on the computer readable medium, which, whenexecuted by the one or more processors, causes the one or moreprocessors to carry out the steps of: determining whether conditions aresatisfied for testing connection state between the apparatus and adifferent network node; if conditions are satisfied for testingconnection state, then sending to the different network node, a DynamicHost Configuration Protocol (DHCP) formatted echo-request message thatincludes an option field that holds data that indicates an echo-requesttype, which when received by the network node causes the network node toreturn a DHCP formatted echo-reply message that includes an option fieldthat holds data that indicates an echo-reply type; determining whetheran echo-reply message that corresponds to the echo-request message isreceived within a particular reply time interval after sending theecho-request message; and if it is determined that the echo-replymessage that corresponds to the echo-request message is not receivedwithin the particular reply time interval, then responding to a loss ofconnection state between the apparatus and the different network node.37. An apparatus as recited in claim 36, wherein the apparatus is one ofa provider network node on premises of a service provider for anInternet Protocol (IP) network and a customer network node on premisesof a customer different from the premises of the provider; and thenetwork node is a different one of the provider network node and thecustomer network node.
 38. An apparatus as recited in claim 37, whereinsaid provider network node executes a gateway server for remote accessto the IP network.
 39. An apparatus as recited in claim 37, wherein saidcustomer network node executes a client for remote access to the IPnetwork.
 40. An apparatus as recited in claim 36, said step ofdetermining whether the echo-reply message corresponds to theecho-request message further comprising determining whether first datain a DHCP header xid field of the echo-reply message matches second datain a DHCP header xid field of the echo-request message.
 41. An apparatusas recited in claim 36, said step of sending the echo-request messagefurther comprising sending an echo-request message that includes in theoption field sender type data that indicates whether execution of theone or more sequences of instructions further causes the one or moreprocessors to carry out the step of a DHCP client or a DHCP server. 42.An apparatus as recited in claim 41, said step of determining whetherthe echo-reply message corresponds to the echo-request message furthercomprising determining whether the sender type data in the echo-replymessage is different from the sender type data in the echo requestmessage
 43. An apparatus as recited in claim 36, said step ofdetermining whether conditions are satisfied for testing connectionstate further comprising determining whether no data packets arereceived from the different network node within a particular keep-alivetime interval.
 44. An apparatus as recited in claim 36, said step ofdetermining whether conditions are satisfied for testing connectionstate further comprising determining whether a DHCP lease is in effectfor configuration data for unicast communications with the differentnetwork node.
 45. An apparatus as recited in claim 37, said step ofresponding to a loss of connection state further comprising attemptingto re-establish a connection state between the apparatus and thedifferent network node.
 46. An apparatus as recited in claim 36, saidstep of responding to a loss of connection state further comprisingnotifying a billing agent process of termination of a session betweenthe apparatus and the different network node.
 47. An apparatus asrecited in claim 36, wherein a Point to Point Protocol (PPP) is not usedfor testing connection state between the apparatus and the differentnetwork node.